Directing Groups And Comparison Of Benzene With Cyclohexene And Phenol

Question 1

What is disubstitution?

Answer 1

When many substituted aromatic compounds can undergo a second substitution.

Question 2

What is an example of disubstitution regarding benzene?

Answer 2

Phenylamine reacts more readily with bromine to produce a multi-substituted product.

Question 3

Why is nitrobenzene less reactive than benzene to from disubstitution?

Answer 3

Nitrobenzene reacts slowly with bromine, requiring both a halogen carrier catalyst and a high temperature. The benzene ring in nitrobenzene is less susceptible to electrophilic substitution itself than in benzene.

Question 4

What does nitrobenzene and bromine produce?

Answer 4

Only one product of 3-bromonitrobenzene.

Question 5

How does the -NH2 in phenylamine react more readily to produce a multi-substituted product with bromine?

Answer 5

Because the -NH2 group activates the ring as the aromatic ring reacts more readily with electrophiles.

Question 6

How does the -NO2 in nitrobenzene react less readily to only produce one substituted product with benzene?

Answer 6

Because the -NO2 group deactivates the aromatic ring as the ring reacts less readily with electrophiles.

Question 7

What is the -NH2 group said to be in terms of directing in substitution?

Answer 7

Positions 2- and 4- directing in the second substituent.

Question 8

What is the -NO2 group said to be in terms of directing in substitution?

Answer 8

Position 3 directing in the second substituent.

Question 9

How are directing groups on substituent groups used to plan organic sysnthesis? (4)?

Answer 9

1. Identify the type of substitution.
2. Identify the directing effect of the two substituents.
3. Write out the two steps with the reagents needed for the synthesis.
4. Is there a mixture of organic products to separate?

Question 10

What is the comparison of benzene with cyclohexene and phenol?

Answer 10

1. Cyclohexene has a localised pi bond above and below the plane of the two carbon atoms. This is electron dense enough to induce dipoles in non-polar molecules, allowing electrophilic attack.
2. Benzene has a delocalised pi bond above and below the plane of the 6 carbon ring. This electron density is not enough to induce dipoles in non-polar molecules, so electrophilic attack can only occur with a catalyst.
3. Phenol also has a delocalised pi bond above and below the plane of the 6 carbon ring and is more electron dense than benzenes so it can induce dipoles in non-polar molecules due to the lone pair of electrons on the O2 group of the OH group, partially delocalising into the pi bond system. It can therefore attract electrophiles more readily to allow electrophilic attack to take place.

Question 11

What effects can different groups attached to a benzene ring have on it?

Answer 11

Can make it more reactive or less reactive AND can direct electrophiles away or towards specific carbons on the ring.

Question 12

What are the 2 activating groups? Reactivity? Direct towards?

Answer 12

NH2 and OH (high electron density). They are electron donating and more reactive than benzene. They direct to the 2,4 and 6 positions of benzene ring.

Question 13

What is the deactivating group? Reactivity? Direct towards?

Answer 13

NO2 (low electron density). Electron withdrawing. Are less reactive than benzene. These direct to the 3 and 5 positions of the benzene ring.

Question 14

How do you make aromatic amines? Conditions?

Answer 14

Nitrobenzene + _ [H] = Phenylamine + H2O:
- Needs tin and concentrated HCl to happen.